This invention relates to radio frequency antenna, and more particularly, to radio frequency antenna adapted to operate with relatively high amounts of power.
As is known in the art, many installations for array antennas impose physical constraints on the size of such an antenna. For example, in an airborne installation, each one of the antenna elements in the array thereof should have minimum depth, width and thickness. Further, in many applications, it is necessary that the antenna operate over a relatively wide bandwidth and handle relatively high amounts of power during transmission of radio frequency energy. One antenna element which has the appropriate size and bandwidth is described in our U.S. Pat. No. 4,353,074 issued Oct. 5, 1982 entitled "Radio Frequency Ridged Waveguide Antenna", assigned to the same assignee as the present invention. As described therein, an open-ended waveguide includes a tapered ridge disposed within the rearward section of the waveguide. The ridge is coupled to a coaxial transmission line for feeding energy into the waveguide. While such an antenna element is adapted to handle large amounts of power and operate over a relatively wide bandwidth, the antenna element has only a single power input and thus the power available for flow into the ridge waveguide antenna, and ultimately transmitted into free-space, is limited to that available from a single source; typically, the output of a travelling wave tube (TWT) amplifier. In those applications requiring feeding more power into each antenna element of an existing array, an external-to-the antenna element power combiner (or hybrid coupler) is used. Thus, the outputs of the plurality of TWT's are fed to the corresponding plurality of power combiner inputs, and the output of the power combiner is then coupled to the antenna element. However, losses occur in the combiner and additional space is required to accommodate such an external-to-the antenna element combiner.